Cold weather affects your boat in several ways, from frozen water inside the engine to weakened batteries, degraded fuel and cracked fiberglass.
Whether you are boating in the winter or putting your boat away for the colder months, proper preparation and a clear understanding of cold weather boating safety are crucial.
This guide explains how freezing weather and cold water temperatures impact your boat and your crew, and how to winterize your boat.
Why Cold Weather Is Hard on Boats
Any water trapped in an engine, hose, pump or fitting can crack components from the inside when freezing temperatures arrive. A low air temperature also thickens fluids, drains battery power, stiffens rubber and plastic, and creates condensation that leads to corrosion.
The damage often stays hidden until the first warm day of spring, when a cracked part starts to leak. Boats that stay in use through the winter months face an added challenge, because wind and water spray can coat decks, rails and gear in ice.
Read Next: Winter Boating Tips
Engine and Cooling System Damage
Frozen water is the most serious cold weather threat to your boat's engine. If water stays in the engine block, exhaust manifolds, risers or raw water pump when temperatures drop below freezing, it can crack the block or housing. That's often one of the most expensive repairs a boat owner can face.
- Inboard and sterndrive engines: Drain the block and manifolds, or flush the cooling system with non-toxic propylene glycol antifreeze.
- Outboards: Tilt the motor down to drain water from the lower unit and cooling passages. Check the gear oil for a milky look, which signals water intrusion.
- Water pumps and hoses: Cold can crack impellers and split hoses. Inspect them before storage and replace any that are worn.
Fogging the cylinders with fogging oil also protects internal engine parts from rust during long periods of inactivity.
Fuel Problems in Winter
Fuel degrades faster than most owners expect. Ethanol-blended gasoline absorbs moisture, and temperature swings cause condensation to form inside a partly empty tank. Over time the water and ethanol can separate from the gas (phase separation), leading to hard starting, rough running and corroded fuel system parts.
To protect your fuel system during cold weather:
- Fill the tank close to full to limit condensation.
- Add a marine fuel stabilizer, then run the engine so treated fuel reaches the carburetor or injectors.
- Replace the fuel/water separator and fuel filters before storage or at the start of the season.
Diesel engines have a different winter concern. Diesel fuel can gel in extreme cold, so use winter-blended fuel or an anti-gel additive if you boat in freezing conditions.
Battery Performance and Electrical Systems
Cold weather reduces battery capacity and slows the chemical reaction that produces power, so a battery that works fine in July may struggle to start your engine in January. A discharged battery can also freeze and crack its case at much higher temperatures than a fully charged one.
- Fully charge batteries before storage.
- Disconnect them or use a marine-grade smart trickle charger.
- Store batteries in a cool, dry place off the ground if you can remove them.
- Clean terminals and apply a corrosion inhibitor.
Check wiring, bilge pumps and navigation lights too. Moisture and freezing temperatures can corrode connections.
Hull, Gelcoat and Fiberglass
Fiberglass itself handles cold temperatures well, so damage usually comes from water freezing in cracks, fittings or onboard systems rather than from the cold itself.
Freeze-thaw cycles can make small problems bigger. Water that seeps into tiny cracks in the gelcoat, around fittings or into a damaged core can freeze, expand and widen those openings. Wooden boats and boats with wood components are also vulnerable to moisture and ice.
You can leave your boat in the water during the winter in some climates, but it takes extra care, and in areas with heavy ice, storing it out of the water is the safer choice. If your boat stays in the water, ice can crush or scrape the hull. A bubbler or de-icer system keeps water moving around the boat and prevents solid ice from forming.
For boats stored on land, make sure the cover or shrink wrap allows airflow and sheds rain and melting snow, because pooled water and heavy snow can damage the boat and the cover.
Plumbing, Livewells and Freshwater Systems
Any onboard system that holds water is at risk. Freshwater tanks, water heaters, faucets, washdown pumps, livewells, baitwells, bilge pumps and air conditioning raw water lines can all freeze and split. Drain these systems completely and, where recommended by the manufacturer, run non-toxic antifreeze through the lines. Leave drain plugs out and keep the bilge dry.
Canvas, Upholstery and Trailer Care
Cold makes vinyl, canvas and clear plastic windows stiff and brittle, so avoid folding or flexing them in freezing weather. Clean upholstery before storage to prevent mildew, and use breathable covers. Don't forget the trailer: check tire pressure and condition, grease the bearings and inspect lights and brakes before you tow in winter or store the boat for the season.
A Simple Cold Weather Boat Checklist
- Drain or protect the engine and cooling system from freezing.
- Stabilize fuel and fill the tank.
- Change the engine oil, lower unit oil and filters.
- Charge and maintain the batteries.
- Drain water from all plumbing, livewells and bilges.
- Wash, wax and cover the boat with a breathable cover.
- Inspect the trailer and store the boat in a dry, covered space if possible.
Frequently Asked Questions
Q: At what temperature does a boat need to be winterized?
A: Winterize your boat before temperatures consistently drop to or below freezing, 32°F (0°C). A single hard freeze can crack an engine block that still holds water, so many boaters winterize as soon as overnight lows approach the mid-30s.
Read Next: How to Winterize a Boat
Q: What should I consider for cold water boating?
A: Cold water boating takes planning for the water as well as the air. Water below about 70°F (21°C) is generally considered cold, and the risk rises sharply as temperatures approach freezing, even if the air feels comfortable.
Check the forecast and water temperatures before you go, dress in layers for staying warm, wear a life jacket, share your float plan and carry a way to call for help. Make sure your boat is properly prepared for the cold as well.
Read Next: Tips for Staying Warm on a Boat
Q: What should I do if someone falls overboard in cold water?
A: Stop the boat, throw a flotation device, keep your eyes on the person and call for help right away. A person in the water should stay calm and focus on controlling their breathing while cold shock passes, then float and conserve body heat.
Once they are back aboard, remove wet clothing, wrap them in dry layers or blankets and seek medical attention, since hypothermia can continue to develop after a rescue.
